Inline Power (also known as Power over Ethernet or PoE) is a technology for providing electrical power over a wired data telecommunications network (such as, for example, the well-known Ethernet) from power source equipment (PSE) to a powered device (PD) over a link section. The power may be injected by an endpoint power source equipment at one end of the link section or by a midspan power source equipment along a midspan of a link section that is distinctly separate from and between the media dependent interfaces (MDIs) to which the ends of the link section are electrically and physically coupled.
PoE is defined in the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) Standard Std 802.3af-2003 published 18 Jun. 2003 and entitled “IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements: Part 3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications: Amendment: Data Terminal Equipment (DTE) Power via Media Dependent Interface (MDI)” (herein referred to as the “IEEE 802.3af standard”). The IEEE 802.3af standard is a globally applicable standard for combining the transmission and reception (collectively: “transceiving”) of Ethernet packets with the transmission and reception of DC-based power over the same set of wires in a single Ethernet cable. It is contemplated that Inline Power will power such powered devices as Internet Protocol (IP) telephones, surveillance cameras, switching and hub equipment for the telecommunications network, biomedical sensor equipment used for identification purposes, other biomedical equipment, radio frequency identification (RFID) card and tag readers, security card readers, various types of sensors and data acquisition equipment, fire and life-safety equipment in buildings, and the like. The power is direct current, floating 48 Volt power currently available at a range of power levels from about 4 watts to about 15 watts in accordance with the standard. There are mechanisms within the IEEE 802.3af standard to allocate a requested amount of power. Other proprietary schemes also exist to provide a finer and more sophisticated allocation of power than that provided by the IEEE 802.3af standard while still providing basic compliance with the standard. As the standard evolves, additional power may also become available. Conventional 8-conductor type RG-45 connectors (male or female, as appropriate) are typically used on both ends of all Ethernet connections. They are wired as defined in the IEEE 802.3af standard.
In accordance with the IEEE 802.3af standard as presently constituted, power source equipment carries out an inline power detection process, and, if successful, an optional inline power classification process. The detection process attempts to detect an identity network present at the powered device. This is usually a 25,000 ohm resistor which is detected by applying a first voltage across the inline power conductors and reading a first current drawn, then applying a second voltage and reading a second current drawn. If the detection process measures the resistance as 25,000 ohms, then a powered device capable of accepting inline power pursuant to the IEEE 802.3af standard is present. Otherwise, it is assumed that a powered device is not present. If such a powered device is present, then under the IEEE 802.3af standard an optional classification process is implemented by applying a third voltage and measuring a third current drawn. The third current drawn characterizes the powered device as a member of one of a set of five IEEE 802.3af classes. Depending upon the class, up to a certain amount of inline power should be provided to the powered device by the power source equipment.
Inline Power is also available through techniques that are non-IEEE 802.3af standard compliant as is well known to those of ordinary skill in the art. The techniques described herein are also generally applicable to systems that are not IEEE 802.3af standard compliant.
In many cases where powered devices are used, it may be desirable to provide some additional capacity to classify powered devices receiving power from power source equipments for at least the purpose of providing more power than is currently contemplated under the IEEE 802.3af standard as well as additional and more precise power gradations.